Lis Valley Irrigation District (Portugal)

Lis Valley Irrigation District (Portugal)

The Lis Valley Irrigation District (LVID) is a state initiative, serving an agricultural area of about 2000 ha; it is located in the Centre of Portugal. The water irrigation sources are the Lis River and its tributaries, and there are no reservoirs. This implies that the flow is very variable over time, depending directly on precipitation. It is normal that the water supply is scarce during the summer season. LVID has a Köppen climate classification type Csb, characterized essentially by temperate and mild summers, and winters of mild temperatures. Rainfall is concentrated mainly from October to March and its average values decrease from the headwaters of the Lis Valley basin towards the coastal region. LVID has an average annual rainfall of 989 mm and an average annual runoff of 378 mm. The dominant LVID soils are modern alluvial soils of high agricultural quality, that in some areas are poorly drained. Salinization problems are frequent in the area, particularly in the lower-laying fields where rice is cultivated.

The main problems of water management faced in collective irrigation and drainage networks, as well as at the field level, are due to the water scarcity and poor quality in the summer, flood risk and poor drainage. In addition, the incipient hydraulic and hydrological information available is not enough to support the Lis Valley Water Users Association for planning and operating the network so that optimization of water productivity is achieved, and farmers’ income is improved.

Rice cultivation has a long tradition in the LVID that has led locally to a significant farmers’ know-how. Rice is presently cultivated in a small area of about 134 ha, mainly due to high water shortage within the irrigation district. The availability of water for rice irrigation is a determining factor for its sustainability. The extent of this problem varies among the productive areas according to hydrological and surface storage conditions. Nonetheless, there is a growing demand for better water use and increased productivity, triggered by competition for water to irrigate other crops or non-agricultural uses. In severely dry years, water scarcity in cultivated land requires more rigorous irrigation water management and policy decision.

The main problems faced by rice irrigation include the following aspects: 1. Limitations in irrigation water availability due to water source scarcity; 2. Constraints on the conveyance hydraulic system, including the energy required for water pumping; 3. Water management problems at distribution and on-farm levels; 4. Environmental risks related with soil salinization and pollution with nitrates; 5. Potential health risks due to low water quality.

This case study aims at contributing to the following objectives: 1. Improving irrigation management at conveyance level, aiming at water saving; 2. Improving irrigation water use at farm level, focusing on the optimization of water productivity related to upgrading soil and crop management techniques, including land levelling; 3. Reducing energy consumption and costs of irrigation water pumping; 4. Decreasing putative health and environmental risks related to irrigation and drainage; 5. Assessing yield impacts and ecotoxicological risks of irrigating with treated wastewater; 6. Improving farmers’ economic outcomes.

This case study will embrace the total rice production area, which is very small, focusing only on the farm’s scale. The study is complemented by laboratory experiments, to investigate the effect of irrigating using treated wastewater on selected rice varieties. The expected impacts of the project are: 1. Increased income of rice farmers due to the improvement of production technologies (water, fertilizers, energy) and a better rice varieties’ selection; 2. Potential increase of the rice irrigated area, allowed by the augment of the amount and quality of the available water resulting from using treated waste water for rice irrigation.